International multi-center randomized controlled trial to examine the effect of growth hormone replacement (hGH) in adolescent and young adult patients with childhood onset growth hormone deficient (GHD)previously treated to final height. Previous data obtained from adult GHD patients of childhood onset treated with hGH until epiphyseal closure indicate that in spite of satisfactory final height results, other developmental milestone may not have been achieved in these individuals. Evidence suggests that the attainment of adult body shape and of peak bone mass are usually not reached until after epiphyseal closure, i.e. after final height has been reached. Thus, patients only treated to final height often have a lower than normal lean body mass, and a lower than normal bone mineral content (BMC) and bone mineral density (BMD). This clinical study will test the hypothesis that continuing hGH replacement therapy for two years after epiphyseal closure will result in increased lean body mass, BMC, and BMD. The accepted daily replacement dosage for adults (0.017-0.034IU/kg/day) will also be evaluated to see if it is significant enough to cover the developmental phase following epiphyseal closure in young adults, or if a larger dosage closer to that used in children (0.070-0.100 IU/kg/day) is more appropriate. Three treatment arms will be included; pediatric dosage, adult dosage, and no treatment.